Chapter 21: The Linux System Operating System Concepts – 8th Edition, Silberschatz, Galvin and Gagne ©2009 Chapter 21: The Linux System Linux History Design Principles Kernel Modules Process Management Scheduling Memoryyg Management File Systems Input and Output Interprocess Communication Network Structure Security Operating System Concepts – 8th Edition 21.2 Silberschatz, Galvin and Gagne ©2009 Objectives To explore the history of the UNIX operating system from which Linux is derived and the principles which Linux is designed upon To examine the Linux process model and illustrate how Linux schedules processes and provides interprocess communication To look at memory management in Linux To explore how Linux implements file systems and manages I/O devices Operating System Concepts – 8th Edition 21.3 Silberschatz, Galvin and Gagne ©2009 History Linux is a modern, free operating system based on UNIX standards First developed as a small but self-contained kernel in 1991 by Linus Torvalds, with the major design goal of UNIX compatibility Its history has been one of collaboration by many users from all around the world , corresponding almost exclusively over the Internet It has been designed to run efficiently and reliably on common PC hardware, but also runs on a variety of other platforms The core Li nux operat ing system kerne l is ent ire ly or ig ina l, but it can run much existing free UNIX software, resulting in an entire UNIX- compatible operating system free from proprietary code Many, v ary ing Linux Distrib u tions inclu ding the kernel, applications, and management tools Operating System Concepts – 8th Edition 21.4 Silberschatz, Galvin and Gagne ©2009 The Linux Kernel Version 0.01 (May 1991) had no networking, ran only on 80386- compatible Intel processors and on PC hardware, had extremely limited device-drive support, and supported only the Minix file system Linux 1.0 (March 1994) included these new features: z Support for UNIX ’s standard TCP/IP networking protocols z BSD-compatible socket interface for networking programming z Device-driver support for running IP over an Ethernet z EhEnhance dfild file sys tem z Support for a range of SCSI controllers for high-performance disk access z Extra hardware support Version 1.2 (March 1995) was the final PC-only Linux kernel Operating System Concepts – 8th Edition 21.5 Silberschatz, Galvin and Gagne ©2009 Linux 2.0 Released in June 1996, 2.0 added two major new capabilities: z Sflilhiildifll64Support for multiple architectures, including a fully 64-bit nat ive Alp ha port z Support for multiprocessor architectures Other new features included: z Improved memory-management code z Improved TCP/IP performance z Support for internal kernel threads, for handling dependencies between loadable modules, and for automatic loading of modules on demand z Standardized configuration interface Ava ila ble for Mo toro la 68000-seriSStdfies processors, Sun Sparc systems, and for PC and PowerMac systems 2.4 and 2.6 increased SMP support, added journaling file system, preemptive kernel, 64-bit memory support Operating System Concepts – 8th Edition 21.6 Silberschatz, Galvin and Gagne ©2009 The Linux System Linux uses many tools developed as part of Berkeley’s BSD operating system, MIT’s X Window System, and the Free Software Foundation's GNU project The min system libraries were started by the GNU project, with improvements provided by the Linux community Linux networking-administration tools were derived from 4.3BSD code; recent BSD derivatives such as Free BSD have borrowed code from Linux in return The Linux system is maintained by a loose network of developers collaborating over the Internet, with a small number of public ftp sites acting as de facto standard repositories Operating System Concepts – 8th Edition 21.7 Silberschatz, Galvin and Gagne ©2009 Linux Distributions Standard, precompiled sets of packages, or distributions, include the basic Linux system, system installation and management utilities, and ready-to-install packages of common UNIX tools The first distributions managed these packages by simply providing a means of unpacking all the files into the appropriate places; modern distributions include advanced package management Early distributions included SLS and Slackware z Red Hat and Debian are popular distributions from commercial and noncommercial sources, respectively The RPM Package file format permits compatibilit y among the various Linux distributions Operating System Concepts – 8th Edition 21.8 Silberschatz, Galvin and Gagne ©2009 Linux Licensing The Linux kernel is distributed under the GNU General Public License (GPL), the terms of which are set out by the Free Software Foundation Anyone using Linux, or creating their own derivative of Linux, may not make the derived product proprietary; software released under the GPL may not be redistributed as a binary-only product Operating System Concepts – 8th Edition 21.9 Silberschatz, Galvin and Gagne ©2009 Design Principles Linux is a multiuser, multitasking system with a full set of UNIX- compatible tools Its file system adheres to traditional UNIX semantics, and it fully implements the standard UNIX networking model Main design goals are speed, efficiency, and standardization Linux is designed to be compliant with the relevant POSIX documents; at least two Linux distributions have achieved official POSIX certification The Linux programming interface adheres to the SVR4 UNIX semantics, rather than to BSD behav ior Operating System Concepts – 8th Edition 21.10 Silberschatz, Galvin and Gagne ©2009 Components of a Linux System Operating System Concepts – 8th Edition 21.11 Silberschatz, Galvin and Gagne ©2009 Components of a Linux System (Cont) Like most UNIX implementations, Linux is composed of three main bodies of code; the most important distinction between the kernel and all other components The kernel is responsible for maintaining the important abstractions of the operating system z Kernel code executes in kernel mode with full access to all the ppyhysical resources of the comp uter z All kernel code and data structures are kept in the same single address space Operating System Concepts – 8th Edition 21.12 Silberschatz, Galvin and Gagne ©2009 Components of a Linux System (Cont) The system libraries define a standard set of functions through which applications interact with the kernel, and which implement much of the operating-system functionality that does not need the full privileges of kernel code The system utilities perform individual specialized management tasks Operating System Concepts – 8th Edition 21.13 Silberschatz, Galvin and Gagne ©2009 Kernel Modules Sections of kernel code that can be compiled, loaded, and unloaded independent of the rest of the kernel A kernel module may typically implement a device driver, a file system, or a networking protocol The module interface allows third parties to write and distribute, on their own terms, device drivers or file systems that could not be distributed under the GPL Kernel modules allow a Linux system to be set up with a standard, minimal kernel, without any extra device drivers built in Three components to Lin ux modu le su pport: z module management z driver registration z conflict resolution Operating System Concepts – 8th Edition 21.14 Silberschatz, Galvin and Gagne ©2009 Module Management Supports loading modules into memory and letting them talk to the rest of the kernel Module loading is split into two separate sections: z Man agin g sectio n s of modu l e code in k ern el m em or y z Handling symbols that modules are allowed to reference The module requestor manages loading requested, but currently unlddloaded, mo dlitldules; it also regu lllarly quer ies thkthe kerne ltl to see whether a dynamically loaded module is still in use, and will unload it when it is no longer actively needed Operating System Concepts – 8th Edition 21.15 Silberschatz, Galvin and Gagne ©2009 Driver Registration Allows modules to tell the rest of the kernel that a new driver has become available The kernel maintains dynamic tables of all known drivers, and provides a set of routines to allow drivers to be added to or removed from these tables at any time Registration tables include the following items: z Device drivers z File systems z Network protocols z Binary format Operating System Concepts – 8th Edition 21.16 Silberschatz, Galvin and Gagne ©2009 Conflict Resolution A mechanism that allows different device drivers to reserve hardware resources and to protect those resources from accidental use by another driver The conflict resolution module aims to: z Prevent modules from clashing over access to hardware resources z Prevent autoprobes from interfering with existing device drivers z Resolve conflicts with multiple drivers trying to access the same hardw are Operating System Concepts – 8th Edition 21.17 Silberschatz, Galvin and Gagne ©2009 Process Management UNIX process management separates the creation of processes and the running of a new program into two distinct operations. z The fork system call creates a new process z A new ppgrogram is run after a call to execve Under UNIX, a process encompasses all the information that the operating system must maintain to track the context of a single execution of a single program Under Linux, process properties fall into three groups: the process’s identity, environment, and context Operating System Concepts – 8th Edition 21.18 Silberschatz, Galvin and Gagne ©2009